Have on hand two 8 inch pie crusts, unbaked. Preheat oven to 375F.
Cream together butter and sugar. Add flour and stir in eggs, one at a time.
Add the walnuts, zest and reconstituted buttermilk and mix well.
Pour into pie crusts and bake for 15 minutes at 375 then decrease to 350 for the remaining time. Watch the edges for over-browning and cover them with foil if needed. Bake until middle is no longer jiggly, about one hour total.